Since its founding in 1985, in response to RFA84-NS-01, the UCSD Multidisciplinary Center for the Study of the Neural Bases of Language, Learning and Behavior has become a major national and international resource in Developmental Cognitive Neuroscience. In the first five years, we have broken new ground by establishing contrasting neurological and behavioral profiles for children suffering from specific language impairment (LI), focal brain lesions (FL), Williams Syndrome (WS), Down Syndrome (DS), as well as an array of rare inborn errors of metabolism (MET). We have demonstrated that these populations display robust patterns of association and dissociation among component processes in language and cognitive development. We have also uncovered some important developmental changes in those patterns, increasing our understanding of developmental changes in the structural and functional organization of the brain. In Years 6-10, we will continue to work with the same populations. Building on results from Years 1 - 5, we have formulated an array of new questions about brain and behavioral development, revolving around (1) patterns of association and dissociation between and within language and other cognitive and communicative domains, (2) the neural correlates of these contrasting profiles, (3) developmental changes in the behavioral and neural profiles that characterize each population, (4) the nature and limits of neural specialization for language and other aspects of cognition, and finally, (5) the complementary issue of plasticity, i.e. alternative forms of organization in the mental and neural processes responsible for language and other cognitive processes in our species. In order to maximize our ability to draw comparisons across populations, we will draw from a common pool of experimental methods that represent the state of the art in cognitive science and neuroscience. In the four neurobehavioral projects, we will continue our focus on language and spatial cognition (the areas emphasized in Years 1 - 5), together with some new initiatives in the areas of attention, memory, and affect. These will be complemented by projects focussed directly on brain structure (using magnetic resonance imaging) and brain function (using event-related brain potentials). Given our interest in developmental trajectories, we will emphasize longitudinal methods in all six projects, across the age range from 4 - 12 years of age. Collaborating institutions include the UCSD Departments of Pediatrics, Neuroscience, Radiology, Psychiatry, Psychology and Cognitive Science, the Center for Research on Language and the Project in Cognitive and Neural Development at UCSD, the Departments of Psychology and Communicative Disorders at SDSU, Children's Hospital (CHHC) and the Salk Institute for Biological Studies.